Abstract

Background

Invalid information on dietary intake may lead to false diet-disease associations.
This study was conducted to examine the relative validity of the food frequency questionnaire
(FFQ) used to assess dietary intake in the Leiden Longevity Study.

Methods

A total of 128 men and women participating in the Leiden Longevity Study were included
in the present validation study. The performance of the FFQ was evaluated using the
mean of three 24-hour recalls as the reference method. Evaluation in estimating dietary
intake at the group level was done by paired t-tests. The relative validity of the
individual energy adjusted level of intake was assessed with correlation analyses
(Pearson’s), with correction for measurement error.

Results

On group level, the FFQ overestimated as well as underestimated absolute intake of
various nutrients and foods. The Bland and Altman plot for total energy intake showed
that the agreement between the FFQ and the 24-hour recalls was dependent of intake
level. Pearson correlation coefficients ranged from 0.21 (alpha linolenic acid) to
0.78 (ethanol) for nutrients and from -0.02 (legumes, non-significant) to 0.78 (alcoholic
beverages) for foods. Adjustment for energy intake slightly lowered the correlation
coefficients for nutrients (mean coefficient: 0.48 versus 0.50), while adjustment
for within-subject variation in the 24-h recalls resulted in higher correlation coefficients
for both nutrients and foods (mean coefficient: 0.69 for nutrients and 0.65 for foods).

Conclusions

For most nutrients and foods, the ability of the FFQ to rank subjects was acceptable
to good.